机械毕业设计英文外文翻译253计算机辅助数控编程应用于非典型零件的加工.docx
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机械毕业设计英文外文翻译253计算机辅助数控编程应用于非典型零件的加工.docx
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机械毕业设计英文外文翻译253计算机辅助数控编程应用于非典型零件的加工
COMPUTER-AIDEDCNCPROGRAMMING
FORTHEMACHININGOFNON-TYPICALPARTS
GrzegorzNikiel
GrzegorzNIKIEL,Ph.D.,Eng.,UniversityofBielsko-Biała,Departmentof
ManufacturingTechnologyandAutomation,43-309Bielsko-Biała,ul.Willowa2,
gnikiel@ath.bielsko.pl
1.Introduction
Manymanufacturingfirms,especiallymediumandsmall,hastosolveproblemofproductiondevelopmentandsearchofnewcustomers.Inmanycasesthisleadstotheassortmentenlargingofalreadymanufacturedproducts.Oftenthisisjoinedwithimplementationofthenewmanufacturingprocesses.InconditionsofmarketcompetitionitdemandshighflexibilitywhichisoftengotinwayreplacingofconventionalmanufacturingresourcesbythemodernCNCtoolmachines[1].Thisisessentialsconditionformoreefficientdevelopment,higherqualityandfasteradoptiontonewrequirements[2].FormaintenanceofthelowcostsofmanufacturingforproductionofsmallandmediumbatchesveryoftentheGroupTechnologyisapplied[3].Withhelpofgroupingofthemanufacturedcomponentsintofamiliesmoreefficientthemachines,devices,workersareused.IntheprocessesplanningonefrommostimportanttasksistheCNCmachinetoolprogramming[4,5].VeryoftentheCAD/CAMsystemsareusedfromreasontheirpossibilityofflexibleprogramming.Inthecaseoftypicalcomponentssuchapproachthepositiveresultsgives,thoughitdemandsanefficientco-operationsbetweenconstructorsandtechnologist.
Sometimesfromdifferentreasonsitisimpossible,especiallywhentheGroupTechnologyisapplied.Usuallythepartprogramsformachiningofsinglecomponentsarecreated,butthemodernCNCcontrollersoffersomemethodsofprogramming,whichtomachiningofsomesimilarcomponentscanbeused.Suchmethodsare:
1.Cycles[6].Thecyclesaredesignformachiningoftypicalsurfaces(theholes,threads,slotsetc.).Usuallyaparametricdescriptionofmachinedsurfacesisappliedwhichenabletheeasyandfastchangesoftheirgeometry.Unfortunatelytheybecharacterizedbysmallflexibilityandsmallinfluenceontostrategyofmachining,dependentonlyfromtheparametersofcycle.InthemoderncontrollersitpermitontoaWorkshopOrientedProgramming(WOP),i.e.programmingdirectlybytheoperators,oftenaidedbyadialogprogramming(sometimesaconversationalprogrammingcalled).Thereforethisisrelativesimpleprogrammingmethod,veryoftenusedinindustrialpractice.
2.Parametricprogramming[5,6].Atypicalpartprogramisexecutedfrombeginningtoendinonerun.Inparametricprogrammingtheexecutionofpartprogramcanrunintodifferentway(e.g.byconditionalinstructionIF..THEN..use).Inaddition,amultiplerepetitionofthepartprogramfragmentisaccessible(REPEATloop,WHILEloopetc.).Furthermore,thearithmeticalfunctionsandotheradvancedfunctionsarepossible.Theaxispositions,feedandspeedfunctions,etc.canbespecifiedbyaparametricexpressions(byR-parametersuse).Intothiswayitwasbeenpossibletocreateownmachiningcyclesalso.Thisapproachdemandshighskillsofprogrammingandisverylabour-consumingalso.Exactverificationoftheprogramisnecessary,inthisitsimmunityinthedangeroussituations(e.g.joinedwithapplicationofincorrectvalueoftheinputparameters).Thereforeinviewofabovementioneddefectsitisinfrequentlyusedinindustrialpractice.
3.Programmingbasedonthefreelydefinedcontours.ThetaskdependsondefiningofmachinedcontouranditsautomaticconversiontotheCNCcodes.Iftheautomaticcutterradiuscompensation(theG41andG42functions)isnotusedthenadditionallyaequidistanthastobegenerated.Thissub-taskiseasytorealizationifmentionedcontourisrepresentedinaCADsystem–withhelpoftheOffsetfunction.Secondsub-taskoftenisrealizedinwayofexportofgraphicformofthetoolpathtothetypicalformatsofdataexchange(DXF,HPGLetc.).Innextstepbythesuitablepostprocessorsuse(forexamplethesolutiongivenin[7])conversionoftoolpathontotheCNCcodesisperformed.Frompracticalregardsthisapproachingeneralityforthesimpleoperationsisapplied,e.g.alasercutting,awaterjetcuttingetc.Asolutionintegratingbothsub-tasksinoneapplicationprogramareappliedalso–theAutoCUTisthebestexample
[8].Inpracticethissolutionisnotappliedtoooftenalthoughitpossessesmanyadvantages.
IntheconditionsofsmallbatchproductionaprocessplanningtotheCNCprogrammingisoftenrestricted[9].InthissituationlargemeaninghasintegrationoftheCAD/CAMsystemswithomissionofCAPPstage.TheFeaturesideaisthenaeffectivemethodofdataexchange[10,11,12].WhentheGroupTechnologyisused,aftersupplementbyappropriatedatabasesandknowledgebases,itcanbebestsolutionforproductionoftypicalelements[13,14].Incaseofnon-typicalpartssuchapproachgenerallyisineffective.MainlyinviewofthewidelyappliedmethodsofFeaturesrecognizingwhichlimitnumberoftheFeaturetypes[10,12].MaybeinfutureasolutionwillbringintegrationofCAD/CAM/CNCsystemsbasedontheSTEP-NCstandards(ISO14649,ISO10303:
238)[15,16]whichwillreplacetraditionallyappliedCNCprogrammingwithG-codesontothingoftheneutralformatofdataexchange.
2.Analysisoftheexamples
PresentedbelowexamplesofthegroupCNCmachiningareafragmentofproductionprogramfromthesmallfirm.Generallythiscomponentshavenon-typicalshapes,theyaremanufacturedfromhardmaterials(e.g.austeniticstainlesssteel),usuallyneededthespecialjigsandfixtures,intheconditionsofsmallbatchproduction.Theplanningprocessesinthiscasedemandaparticipationoftechnologistswithlargeexperience.AspecificcharacterofaccessibletoolmachinesfordefiningofthemethodofCNCprogrammingshouldtoconsideralso.Afterexecutionofdetailedanalysisontosubjectofthediscussedmethodsthefollowingconclusionswereformulated:
•Themachinedshapesexcludeapplyingofthestandardcycles.Mostoftheprogramsisdesignforthecomplicatedprofilesmachining.Fromheredescriptionoftheseprofilesislargestproblem.Moreover,machiningofthecomponentsisperformedonthedifferenttoolmachines,equippedindifferentcontroller.
•Formostofmachinedcomponentstheexactdrawingdocumentationisnotmade.Inaproductionorderthegeneraldrawingsareincluded,oftendescribedbyparametricdimensions.Thencurrentvaluesofthisparametersaregivenalso.
•Shortseriesandlargevarietyofthecomponentsdemandsfastmodifyingofcurrentproductionprogram.FastCNCprogrammingandtheprogramsimplementationisnecessary,bestdirectlyattoolmachine(WOP).
•Oftentheoperatorsoftoolmachinespossesslargeknowledgeandexperienceintheareaofmanufacturingtechnology,sufficientforpreparationofsimpleprogram(inrangeofthetechnology).Fastpreparationofthetoolpathislimitationonly.
Generalconclusionissuch,thatinpresentedcaseuseoftheuniversalCAD/CAMsystemsforCNCprogrammingisverydifficult.Moreover,itjoinswithhighcostsofshoppingandtrainingsfortheworkers.Lowflexibilityofthismethodisexpectedalso,especiallytimeofprogrammingcanbeagreatproblem.Inthissituationaparametricprogrammingasthebestsolutionwas
considered.But,asitwasshewontheexamples,theparametricprogrammingcanberealizedindifferentway.
2.1.ExampleI–thegroovedrollersfinishmachining
Finishmachiningofthegroovedrollersfamilywassubjectofresearch(Fig.1).Basicchangingdimensionsforrollerswereexternaldiameterd,workingprofilelengthLandprofileangleα.Theprofileofco-operaterollerismovedbyhalfpitch.FinishmachiningisperformedbyturningwithuseoftoolwiththeVtyperhombicinsert(noseangleequal35°),wherethenoseradiusrεisequal0,4mm(Fig.1).Thetoolreferencepointislocatedintheinsertnosecenter.ForeachpairofrollerstheirprofileisdesignedinaCADenvironmentaccordingtothedimensionsofrollingelements.Afastmethodoftoolpathgenerationwasthemainsubjectofperformedresearch.Firstofallgeneratingofthetoolpath(onlyfinishing,withoutroughmachiningwhichisprogrammedinamanualmode)andformingitinaccordancewithrequirementsofappropriatelanguage.Ashasbeenmentionedabovetheuseofparametricprogramwasconsidered.Withhelpoftheadvancedprogrammingmethods(e.g.transformationsofco-ordinatesystem,sub-programsetc.)itwasbeenpossibletoachievementtheaimofthisstudy.However,numberofthemachinedrollersisverysmall(someperyear).Thereforeanotherapproachwasaccepted.BecauseforeachrolleraexactCADmodelisprepared(2Dmodel),itwasusedtoCNCprogramming.Forachievementofthisaimthefollowingactivitieswasconsidered:
•ForeachusedCNCcontrollertheframeworkofpartprogramiscreated,includingprogramheader,technologicalfunctions,toolfunctionsandprogramend(withouttoolpath).
•InaCADenvironmentthemodelco-ordinatesystemisassignedtotheworkpiececo-ordinatesystem.
•Inthesemi-automaticmodefromthemodelofworkingsurfaceatoolpathisextractedwithusetheOffsetfunction.
•Manuallytherun-inpathandtherun-outpathisadded.Fordifferentelementsoftoolpath(withworkinginterpolationorwithrapidinterpolation)differentattributesoflinewereapplied.
•Thedesignedtoolpathisconvertedtoanumericalforminsemi-automaticmodebyspecialprogram(writteninLISPlanguage)andinsertedtothepartprogram(createdpreviously).Userhastoshowonlyfirstelementofthetoolpath,furtheranalysisisworkedoutonbasisofthedrawingdatabas
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